Field of the Invention
The invention relates to a device for applying a liquid to a print carrier sheet, in particular a printing or varnishing unit in a sheet-fed rotary printing machine. The printing or varnishing unit includes an applicator cylinder and an impression cylinder assigned to the applicator cylinder.
In the field of web-fed rotary printing, in particular in the flexographic and offset printing, printing form and rubber blanket sleeves are used in order to avoid vibrations and the spoilage which is caused by a clamping channel in the case of conventionally clamped printing plates and rubber blankets and occurring as a result of wide regions free of any printing image on the print carrier web.
Published, Non-Prosecuted German Patent Application DE 36 33 155 A1 describes a flexographic printing form cylinder having a sleeve which carries a printing block. Although the sleeve is simple to produce, the printing form cylinder can be used only in web-fed rotary printing, since the grippers, necessary in sheet-fed rotary printing for conveying the print carrier sheets on the impression cylinder, would collide with the printing block and destroy it.
Published, Non-Prosecuted German Patent Application DE 31 17 855 A1, corresponding to U.S. Pat. No. 4,399,767, describes a varnishing unit in a sheet-fed rotary printing machine, the applicator roller of which has a recess on the circumference in the axial direction. The recess allows the passage of the gripper units of the chain conveyor. The applicator roller is equipped with a plate clamping device, by which plates having either a smooth or an engraved surface can optionally be clamped. Furthermore, the block roller and the impression roller are disposed in such a way that their gaps coincide with the recess in the applicator roller during rotation. Although this varnishing unit can be used in sheet-fed rotary machines, clamping of the plates is complicated.
Furthermore, German Patent DE 43 07 320 C1 describes a printing machine for indirect printing methods, in which the rubber blanket sleeve can be pushed through an orifice in the machine side wall. Although it is possible to exchange the sleeve in a simple way in the printing machine, it is not possible for the rubber blanket sleeve, which has a closed circumferential surface without any gap(s), to be used in sheet-fed rotary printing machines.
Moreover, varnishing units configured for flexographic printing units are known in sheet-fed offset machines. In contrast to web-fed rotary printing, instead of sleeve systems, varnishing plates and varnishing blankets are clamped onto a cylinder in a similar way to sheet-fed printing units. These plates are difficult to produce and present handling problems. In order to clamp the plates and blankets so as to have an accurate fit, complicated plate supply devices and clamping devices are required. On account of the warping of conventional flexographic plates, varnishing plates with an aluminum carrier are employed. For drawing them onto the cylinder, a pressure roller is used, which may damage the relief of the polymer plate if an excessive pressing force is exerted. In the case of a relatively large sheet format, it is necessary to have two operators. Therefore, in-register fitting of the plates requires a high outlay.